The Study On The Effect Of Alloy Elements On The Microstucture And Corrosion Behavior Of Deformation Mg-Bi Based Alloy

Mg alloys are of industrial interest as structural metals due to their low density and high strength to weight ratio.In addition,magnesium alloys have attracted researchers in medical field due to its good biocompatibility,mechanical compatibility and biodegradability.However,the key obstacle hindering widespread application of magnesium alloys is mainly related to the poor corrosion resistant,especially in the human body liquid environment,which accelerated the corrosion rate.The corrosion resistance and mechanical property of magnesium alloys can be improved by addition of non-toxic alloying elements and deformation processing.It provides a method for the development of new medical magnesium alloy.Therefore,the corrosion resistance and mechanical property of alloys is improved by adding Sn,Al and Zn alloy elements to Mg-Bi alloys as well as rolling and extrusion deformations in this study.In addition,in order to obtain the best comprehensive performance of the good mechanical properties and corrosion resistance,the corrosion and strengthening mechanisms of the alloys were revealed through the microstructure,corrosion morphology and tensile properties analyses.The results show that:?1?The microstructure evolution and properties of as-rolled Mg-6Bi-xSn?x=0%?1%?2%?3 wt.%?were studied.The results revealed that hardness value of the alloy increases with the increase of Sn content,this is mainly attributed to the synergistic effect of small grain and dispersion distribution of the second phase particles,however the corrosion rate decrease firstly and then increase later is mainly due to the competitive between grain refinement which reduce the corrosion rate and more second phase particles which increases the corrosion rate,Mg-6Bi-2Sn alloy shows the best comprehensive performance due to its uniform structure.?2?The corrosion behaviors of as-cast and as-rolled Mg-6Bi-2Sn alloys were investigated and the influence of the microstructural characteristics on the corrosion properties were discussed,to further investigated the reason to improved the corrosion resistance of the as-rolled alloy.After rolling,remarkable grain refinement and uniform distribution of second phase particles could be achieved,the corrosion mechanism from intergranular corrosion?as-cast?change to pitting corrosion?as-rolled?,the electrochemical and immersion tests results indicated that the as-rolled alloy has a significantly lower corrosion rate,which is mainly attributed to refined grain size,finely dispersed secondary phase particles,favorable crystal orientation and the formation of passivity film.?3?In order to avoid micro-galvanic corrosion caused by the second phase particles,the dilute Mg-1Bi-1Al-1?wt%?Zn alloy was successfully extruded,the dependence of corrosion behaviors and tensile properties on microstructural characteristics of the extruded alloy has been investigated in this paper.The extruded alloy mainly composed of micro scaled?-Mg dynamically recrystallized?DRXed?grains and strongly textured coarse unDRXed grains as well as nano scaled Mg₃Bi₂ precipitates.Note that most of the basal planes are distributed parallel to extrusion direction.the as-extruded alloy presented local corrosion characteristic,the corrosion mechanisms were illustrated and analyzed in terms of grain size,crystallographic texture as well as the corrosion products.